Question: Which of these numbers is prime? ${34,\ 69,\ 75,\ 89,\ 91}$
A prime number has exactly two factors: 1 and itself. The factors of 34 are 1, 2, 17, and 34. The factors of 69 are 1, 3, 23, and 69. The factors of 75 are 1, 3, 5, 15, 25, and 75. The factors of 89 are 1 and 89. The factors of 91 are 1, 7, 13, and 91. Thus, 89 is a prime number.